Digitally reproduced video and audio, namely digital contents, can be copied without deterioration in quality. In order to protect the rights of a copyright holder, many copyright protection systems have been proposed.
One example of such systems is a serial copy management system (SCMS) that limits the number of times a digital content can be copied from a recording medium, such as a compact disc (CD) and a digital versatile disc (DVD).
Another example is Secure Digital Music Initiative (SDMI) that restricts distribution of the digital content, such as music, via the Internet. SDMI limits the number of times the digital content can be copied from a server apparatus (hereafter, simply “server”) to a different apparatus or a recording medium, such as a mini disc (MD).
In recent years, broadcast stations distribute CCI (Copy Control Information)-added contents by a digital broadcasting system (e.g., BS digital, CS digital and terrestrial digital broadcasts) to restrict copying of the contents. CCI is information that restricts copying of content; with CCI, it is possible to restrict an unauthorized person from copying the content, and to limit the number of times the content can be copied.
The above are examples of methods for protecting the rights of a copyright holder pertaining to the distribution of the digital content.
On the other hand, restricting the copying of the content may lead to a situation where a user finds it inconvenient to watch or listen to the distributed content.
Such a situation is, for example, when the user has no freedom to choose an apparatus to play the content with because there are restrictions imposed on the copying of the content.
In recent years, digital household appliances are connected to one another via a network so as to establish a home network, in which digital data can be freely exchanged between the digital household appliances. Moreover, the development of various types of mobile apparatuses has even enabled family members to watch or listen to the content outside the network.
Regardless of such technological advances, there still are cases where the user cannot enjoy the content to the fullest extent even in the network, because copying of the content is permitted only once and thus further copying of the content is entirely restricted. For example, if the user has content that only allows a first-generation copy thereof, once the user copies the content to a personal computer, the user cannot make further copies of the content anymore. With further copying of the content disabled, the user cannot take the content outside the network by copying the content to a mobile device.
In light of the above disadvantages, engineers have developed technology for enabling copying of content within the home network while protecting the rights of a content holder. According to this technology, a copy-restricted content is registered in an in-home server. This structure allows copying of the content with the in-home server controlling copies of the content within the home network (ref. patent document 1). In terms of the earlier example, this technology permits the content to be copied to the mobile device under the condition that the copy of the content in the personal computer gets invalidated. This technology also permits the content to be moved from one server to another under the condition that copies of the content that has been stored in the server do not exist.
[Patent document 1]
Japanese Laid-Open Patent Application Publication No. 2004-54988